C10,

Barry's number is 01751 473124.

He makes two part tubes. There is a split collar that clamps onto the muzzle; the front half overhangs the muzzle to hold the tube. For an 1813 Barry supplies a brass pin that screws into the foresight block holes. Ahis engages in a slot in the collar to ensure the tube is vertical (or at least the same angle as the factory foresight). The tube itself has a small locator pin that engages with the front of the clamp. Barry will cut what ever dovetail you like on the clamp.

The tube can be removed for cleaning and replaced with no loss of zero. I use a strip of j-cloth on a 12 bore brush to clean mine, very quick and easy.